Bacterial plasmids of agricultural and environmental importance

Many important characteristics of bacteria are determined by relatively small genetic elements known as bacterial plasmids. Such agriculturally and environmentally important bacterial characteristics as multiple antibiotic resistance in animal pathogens, nodulation and nitrogen fixation in Rhizobium—plant symbioses, crown gall formation by plant pathogenic Agrobacterium species and pesticide degradation by members of the genus Alcaligenes have been shown to be carried as part of transmissible plasmids. The widespread use of antibiotics in human and veterinary medicine and agriculture has resulted in the evolution and spread of multiple drug resistance plasmids. The problem of drug resistance might be overcome by reduction or pronhibition of the use of clinically important antibiotics for non-therapeutic purposes such as growth promotion or prophylaxis. An understanding of the role of plasmid-borne nitrogen fixation/nodulation characteristics of Rhizobium species may provide an alternative to the use of very expensive nitrogenous fertilizers. Studies of the plant pathogenic Agrobacterium have led to successful biological control of crown gall. Finally, the manipulation of pesticide degrading plasmids has already demonstrated their potential for reducing environmental pollution resulting from the widespread use of complex synthetic molecules in both industry and agriculture.